Mysterious Liquid

Science
Science brain teasers require understanding of the physical or biological world and the laws that govern it.

Zona, the nutty professor, gathered the class one day for an experiment. Zona began, "I have in my hands a rock and a piece of wood. I am going to place them in this beaker of mysterious liquid, and you may observe what happens." Surprisingly, the rock floated and the wood sank! He turned to the class and said, "My question is: What is this mysterious liquid in the beaker?"

Do you know the answer?

Hint

This liquid occurs naturally.

Answer

The mysterious liquid is water. The rock is pumice or volcanic glass which floats in water and the wood was from the desert ironwood tree which is so dense that it actually sinks in water.